Low voltage cold cathode discharge type display devices with metal oxide cathode and phosphor anode matrix

ABSTRACT

A plurality of anode electrodes coated with a phosphor and cathode electrodes coated with an electron emissive substance are disposed at right angles on both sides of an insulative spacer having a plurality of perforations which are arranged in a matrix between a pair of substrates, at least one of them being transparent. Each anode electrode is arranged to face one column of the matrix and each cathode electrode is arranged to face one row of the matrix. The peripheries of the pair of substrates are sealed to form an envelope and the envelope is filled with an inert gas. Switching means is provided for applying an operating voltage across selected anode and cathode electrodes thereby causing the phosphor to luminescence at the cross-point between the selected anode and cathode electrodes.

1 1 June 17, 1975 United States Patent 11 1 Sasaki et a1.

Hubert et al. 313/108 B 313/108 R 2 93? 648 4/1960 Bentley 3,559,1901/1971 Bitzer et al..,..... 3,589 789 6/1971 LOW VOLTAGE COLD CATHODEDISCHARGE TYPE DlSPLAY DEVICES WITH METAL OXlDE CATHODE AND PHOSPHORANODE MATRIX [75] Inventors: Rentaro Sasaki; Akinori Watanabe,

both of Takasaki; Tatsuo Ogasawara, Tokyo; Hidetoshi Sogabe, Gyoda, allof Japan Primary Examiner-Marshall M. Curtis Attorney, Agent, orFirmCharles E. Pfund, Esq.

[57] ABSTRACT A plurality of anode electrodes coated with a phosphor andcathode electrodes coated with an electron emissive substance aredisposed at right angles on both sides of an insulative spacer having aplurality of perforations which are arranged in a matrix between a d ."tL t u LO C PM D w m a w u i d1 mmw C k If. new c e mw .la kkm OOb s C Bn .w S S A H 7 .l

[22] Filed: Apr. 5, 1973 [21] Appl. No.: 348,249

pair of substrates, at least one of them being transparent Each anodeelectrode is arranged to face one col- L0 N OT 74 6 2 9 3 6 M ,RI 0 L W4 O1 BHE] .6 .6. V 5 T m ,89 9 HROO m 6 6 M I 1 V1100 3 mum .9 3 M H .N4 m m3 u u m E 4 R4 3 H l 0 C 4 m3 k UImF H N 555 [56] References CitedUNITED STATES PATENTS cross-point between the selected anode and cathodeelectrodes.

2,049,763 8/l936 DeForest....4....,......v.... SIS/I69 TV 2 926,2862/1960 Skellett 313/108 B 5 Claims, 5 Drawing Figures aasaeoaPATENTEIJJUN 17 ms FlGZA LOW VOLTAGE COLD CATHODE DISCHARGE TYPE DISPLAYDEVICES WITH METAL OXIDE CATIIODE AND PHOSPI-IOR ANODE MATRIX BACKGROUNDOF THE INVENTION This invention relates to a cold cathode discharge typedisplay device wherein a plurality of spaced apart cold cathodeelectrodes and a plurality of spaced apart anode electrodes are arrangedin a matrix and selected cross-points between the electrodes are causedto discharge to display a desired pattern.

However, as the breakdown voltage or the discharge initiating voltage ofthe prior art cold cathode discharge display device is high, it isnecessary to use a drive source of high potential of the order of I80volts, for example, and it has been impossible to drive the displaydevice directly by a transistor. Moreover, since in this type of thedisplay device, display is made by the light of discharge, it has beenimpossible to obtain a variety of colours.

SUMMARY OF THE INVENTION It is an object of this invention to provide animproved cold cathode discharge type display device which can be drivenby a low voltage and can produce a variety of discharge colours of highbrightness.

In accordance with this invention, there is provided a cold cathodedischarge type display device compris ing a pair of substrates, at leastone of them being transparent. an insulative spacer disposed between thepair of substrates and provided with a plurality of perforations whichare arranged in a matrix, a plurality of cold cathode electrodesdisposed between one substrate and the insulative spacer with each coldcathode electrode opposed to one row of the matrix, and electronemissive substance coated on respective cold cathode electrodes, aplurality of anode electrodes disposed between the other insulativesubstrate and the insulative spacer with each anode electrodeopposed toone column of the matrix, means for hermetically sealing the peripheriesof the pair of substrates thereby forming a sealed envelope, an inertgas sealed in the envelope, and means for applying an operating voltageacross selected anode and cathode electrodes so as to establish electricdischarge at the cross-point between the selected anode and cathodeelectrodes. A phosphor for emanating a selected colour is applied onrespective anode electrodes, or on the inner surface of respectiveperforations or on the inner surface of the transparent substrate atportions thereof facing to the anode electrodes. The use of phosphordecreases the breakdown voltage of the display device and emanates adesired colour at a high brightness.

DESCRIPTION OF THE DRAWINGS The invention can be more fully understoodfrom the following detailed description taken in conjunction with theaccompanying drawings in which:

FIG, I is a perspective exploded view of certain essential elements ofthe cold cathode discharge type display device embodying the invention.

FIG. 2 is a cross-sectional view of a portion of the cold cathodedischarge type display device shown in FIG. 1:

FIGS. 2A and 2B show modifications: and

FIG. 3 shows a connection diagram of the driving circuit utilized tooperate the novel display device.

DESCRIPTION OF THE PREFERRED EMBODIMENT With reference now to FIG. 1 ofthe accompanying drawing, the cold cathode discharge type display device1 shown therein comprises a pair of opposing insulative substrates 2 and3, at least one of them being transparent, and an insulative spacer 5disposed between the substrates and is provided with a plurality ofperforations 4 arranged in a matrix. A plurality of anode electrodes 7respectively coated with phosphor films 6 are arranged in parallel witheach other between the upper substrate 2 and spacer 5 with each anodeelectrode opposed to a column of the perforations 4. The phosphor film 6is a mixture, for example, of sili-. con' oxide zinc and manganese (ZnSiO, Mn), sulphate zinc and silver (ZnS Ag), or sulphate cadmium zincand silver (ZnCdS Ag).

Similarly, a plurality of cold cathode electrodes 8 are disposed betweenthe lower substrate 3 and spacer 5 with each cathode electrode opposedto a row of the perforations 4. As shown, cold cathode electrodes 8 andanode electrodes 7 intersect with each other at right angles. The coldcathode electrodes 8 are made of nickel wires or 42-6 alloy wires forthe purpose of improving the bond with glass when the cathode electrodesare sealed with glass as will be described later. Further, to improveelectron emission each cathode electrode is coated with a film of bariumcarbonate BaCO- calcium carbonate CaCO strontium carbonate StCO or thelike and these carbonates are converted into a film of oxide 9 ofbarium, calcium or strontium as will be described later...

After laminating these elements as shown in FIG. 2, the periphery of theassembly is sealed with a binder such as frit glass to form an envelope.Thereafter, the interior of the envelope is evacuated through a suitableexhaust pipe, not shown, and a voltage of about 8 volts, is impressedacross respective cathode electrodes to cause them to generate heat. Bythis heating the barium carbonate, calcium carbonate or strontiumcarbonate is converted into a stable oxide 9. Then, an inert gas such asxenon, argon or mercury is introduced into the evacuated envelope thuscompleting the cold cathode discharge type display device I.

When a voltage of 10 to 20 volts is impressed across selected ones ofthe anode and cathode electrodes 7 and 8, electric discharge will occurat the cross-points between the selected electrodes through aperforation 4 corresponding to the cross-point, The discharge excitesthe phosphor 6 on the anode electrode 7 at a portion corresponding tothe particular cross-point thereby causing the phosphor to luminescence.The phosphor ofa mixture of silicon oxide zinc and manganese (Zn SiO,Mn), sulphate zinc and silver (ZnS Ag), and sulphate cadmium zinc andsilver [ZnCdS Ag) luminescence in green, blue and red. respectively.Thus, it can be noted that perforations 4 in the spacer 5 act asdischarge cells,

FIG. 3 shows a connection diagram of the driving circuit for the novelcold cathode discharge type display device. There is provided a firstrotary switch 10 having a plurality of stationary contacts 10a through[On which are connected to cold cathode electrodes 80 through 8n,respectively, and a second rotary switch ll having a plurality ofstationary contacts llu through lln which are connected to anodeelectrodes through 7n. respectively, of the cold cathode discharge typedisplay device I. An electric source 12 is provided with its positivepole connected to the movable contact llm of the second rotary switch lland its negative pole connected to the movable contact lmof the firstrotary switch through a current limiting resistor 14 and a transistor13. The first and second rotary switches are synchronized to operatestepwisely.

in operation, when a negative input signal is impressed on the baseelectrode of transistor 13, the transistor is rendered conductive toapply the voltage of the source 12 across one of the cathode electrodes8a through 8n selected by the first rotary switch and one of the anodeelectrodes Ila through lln selected by the second rotary switch I]whereby the oxide 9 on the selected cathode electrode emits electrons.These electrons excite the inert gas in a corresponding discharge cellthus initiating discharge between the selected anode and cathodeelectrodes. Consequently, the phosphor 6 at the selected cross-pointluminescences. when the rotary switch 10 is rotated while transistor 13is conductive. the cross-points on respective rows are caused toluminescence successively.

In this manner, by applying to the base electrode of transistor 13 asignal which is synchronized with the operation of the second rotaryswitch 11 and correspond ing to a desired pattern. respectivecross-points are caused to selectively luminescence. If such selectionis performed at such a high speed that can prevent flicker, it would bepossible to display the desired pattern.

By changing the type of the phosphor 6 coated on the anode electrodes itis possible to display the pattern with different colours. Moreover,when compared with the prior art display device of the type wherein thelight per se of the discharge is used to display a pattern it ispossible to drive the display device with a lower voltage and yet toproduce luminescence of higher brightness.

Instead of applying the coating of the phosphor on respective anodeelectrodes. the phosphor can also be applied to one substrate 2 as shownat 6 in FIG. 2A, or on the inner surfaces 6" of the perforations 4 asshown in FIG. 2B.

As above described. the invention provides an improved cold cathodedischarge type display device having a low break-down voltage hence canoperate with a low driving voltage of the order of [0 to volts. Further.in accordance with the invention as a phosphor is caused to luminescenceby electrons emitted from cold cathode. it is not only possible tooperate the display device at a lower voltage than the prior art displaydevice but also to increase brightness.

What is claimed is:

l. A cold cathode discharge type display device comprising a pair ofinsulative substrates. at least one of the substrates being transparent,an insulative spacer disposed between said pair of substrates, saidspacer being provided with a plurality of perforations which arearranged in a matrix, a plurality of cold cathode electrodes disposedbetween one substrate and said insulative spacer with each cold cathodeelectrode opposed to one row of the matrix. an electron emissive metaloxide coated on respective cold cathode electrodes, a plurality of anodeelectrodes disposed between the other insulative substrate and saidinsulative spacer with each anode electrode opposed to one column of thematrix, means for hermetically sealing the peripheries of said pair ofsubstrates thereby forming a sealed envelope. an inert gas sealed insaid envelope, and means for applying an operating voltage across aselected one of the anode electrodes and a selected one of the cathodeelectrodes so as to establish electric discharge at the cross-pointbetween said selected anode and cathode electrodes thereby displaying adesired pattern.

2. The display device according to claim 1 wherein a phosphor is coatedon respective anode electrodes.

3. The display device according to claim 1 wherein a phosphor is appliedon the inner surface of the transparent substrate at least the portionsthereof facing to said anode electrodes.

4. The display device according to claim 1 wherein a phosphor is coatedon the inner surfaces of said perforations.

5. The display device according to claim I wherein said means forapplying said operating voltage comprises a first rotary switch having aplurality of stationary contacts connected to respective cathodeelectrodes, a second rotary switch having a plurality of stationarycontacts connected to respective anode electrodes. and a source ofsupply and a transistor which are connected in series across the movablecontacts of said first and second rotary switches.

1. A cold cathode discharge type display device comprising a pair ofinsulative substrates, at least one of the substrates being transparent,an insulative spacer disposed between said pair of substrates, saidspacer being provided with a plurality of perforations which arearranged in a matrix, a plurality of cold cathode electrodes disposedbetween one substrate and said insulative spacer with each cold cathodeelectrode opposed to one row of the matrix, an electron emissive metaloxide coated on respective cold cathode electrodes, a plurality of anodeelectrodes disposed between the other insulative substrate and saidinsulative spacer with each anode electrode opposed to one column of thematrix, means for hermetically sealing the peripheries of said pair ofsubstrates thereby forming a sealed envelope, an inert gas sealed insaid envelope, and means for applying an operating voltage acrosS aselected one of the anode electrodes and a selected one of the cathodeelectrodes so as to establish electric discharge at the cross-pointbetween said selected anode and cathode electrodes thereby displaying adesired pattern.
 2. The display device according to claim 1 wherein aphosphor is coated on respective anode electrodes.
 3. The display deviceaccording to claim 1 wherein a phosphor is applied on the inner surfaceof the transparent substrate at least the portions thereof facing tosaid anode electrodes.
 4. The display device according to claim 1wherein a phosphor is coated on the inner surfaces of said perforations.5. The display device according to claim 1 wherein said means forapplying said operating voltage comprises a first rotary switch having aplurality of stationary contacts connected to respective cathodeelectrodes, a second rotary switch having a plurality of stationarycontacts connected to respective anode electrodes, and a source ofsupply and a transistor which are connected in series across the movablecontacts of said first and second rotary switches.